Tiltrotor aircraft have been constructed in the past. Such aircraft include one or more engines that pivot from a position that is normal for propeller driven aircraft to a position that is normal for the rotor position of helicopters. The advantages of tilting the engines in this fashion are that the aircraft can take off and land vertically, hover when desired, fly more like an airplane in level flight, and obtain speeds greater than normally possible with helicopters.
The term "proprotor" is utilized herein to describe the airscrew since the airscrew provides the attributes of a propeller when in the level flight position and the attributes of a helicopter rotor when in the vertical position.
With dual engine tiltrotor aircraft, it is highly desirable to be able to provide power to both proprotors from either engine throughout the tilt range of the engines. The tilt range of the engines generally will be from about horizontal or 0 degrees to just past vertical or about 110 degrees.
Due to the desirability of providing power from either engine to both of the proprotors, apparatus must be provided for transferring the power. Since the engines are generally and in this instance located on the ends of the wings, any power transmission mechanism extending between the engines must extend along or through the wings. Accordingly, such apparatus is subjected to the angles of the sweep design of the wing plus the wing dihedral angle plus any flexure of the wing during operation.
It is also highly desirable to be able to provide redundant sources for electrical and hydraulic systems and to be able to power apparatus normally driven by the auxiliary power unit when the engines are not running. Such apparatus is necessarily relatively bulky and heavy and, thus, is preferably located somewhere other than adjacent to the wing tip mounted engines. The engines will, of course, have redundant electrical and hydraulic systems power available.